This invention concerns mechanical transmissions and more particularly transmissions adapted to drive washing machine components.
Modern washing machines typically are arranged with an extraction basket disposed within an outer surrounding tub, with an agitator disposed within the interior of the basket. The washing and rinsing action is achieved by slow oscillation of the agitator, with the items to be washed dispersed in a washing solution contained within the tub and basket.
In order to provide centrifugal extraction of the washing solution after wash and rinse cycles, the basket is spun at a relatively high rate of rotation. The agitator and basket have been driven in certain prior art designs by a highly satisfactory arrangement including an electric motor driving the input of a washing machine transmission, which transmission provides both outputs necessary to achieve the high speed basket spin and the low speed oscillation of the agitator.
Such an arrangement and transmission is disclosed in U.S. Pat. No. 2,844,225, assigned to the assignee of the present application.
The transmission includes clutching producing a low speed oscillation of an output shaft in the first direction of rotation of the motor, which output is connected to an agitator power shaft. In the opposite direction of rotation of the drive motor, the clutching arrangement produces a direct drive to the basket in order to carry out centrifugal extraction.
The oscillatory output is achieved by a mechanical motion which typically involves reciprocation of a gear rack which in turn produces the output oscillation of a pinion gear in mesh with the gear rack. This design has been highly successful and employed for many years in commercial washing machines.
The use of a mechanical movement in order to achieve the conversion of rotation to oscillation of the drive input to the agitator power shaft necessitates rather complex components which represent a significant cost item.
Other approaches to providing oscillatory drive for washing machines have included the use of a reversing electric motor as described in U.S. Pat. No. 2,656,702.
More recently, there has been proposed the utilization of a particular drive motor design which may be commutated in order to produce either unidirectional rotation or cyclically reversing rotational motion. Such capability of the drive motor creates the possibility of providing a direct drive to achieving spin of the basket and oscillation of the agitator by the single electric motor. Even with such motor design, a suitable transmission must be employed in order to provide a direct high speed drive to the basket, while providing a reduced drive of the drive motor to the agitator to produce a reduced speed oscillation.
Since with this type of drive the reversal of the direction of drive cannot be used to produce shifting between the oscillatory and the spin drive modes, it is necessary to provide a separate shifting mechanism. It is advantageous to provide such shifting mechanism which is located externally of the transmission housing in order to eliminate the need for separate sealing of the control levers, etc.
It is important for such home applicance applications to provide a relatively low cost, simple and reliable structure such as to realize the potential advantage of lowering of cost by the use of such a reversing electrical motor, while insuring adequate reliability of the transmission.
An additional consideration in the design of such transmissions is the inertia of the rotating parts exhibited during oscillation of the drive, since the rapid reversal of the motor renders the inertia load relatively significant on those components driven during the agitation cycle.
Accordingly, it is an object of the present invention to provide a washing machine transmission providing an output drive to the washing machine basket and agitator, respectively, adapted to be driven by an input drive motor which is operated to produce unidirectional rotation or cyclically reversing rotation to produce oscillation of the agitator in the agitation mode and relatively high speed rotation of the basket during the spin extraction operation.
It is a further object of the present invention to provide such a washing machine transmission in which the shift between the spin and agitate modes is executed by a shifter arrangement which is located externally of the transmission housing.
It is still a further object of the present invention to provide such a washing machine transmission which is relatively simple in configuration.